Funds are requested for the purchase of a Leica TCS SP8 AOBS 405 UV Spectral Confocal Microscope to be used in the PNB Confocal Facility in the Department of Physiology and Neurobiology at the University of Connecticut, Storrs. The Department currently has a Leica TCS SP2 Spectral Confocal Microscope, which was purchased in 2001 with funds from NIH (1S10RR015684-01). The instrument is maintained as a departmental facility that is open to the entire Storrs campus community. During the past eleven years, it has been heavily used, averaging 7 hours a day, resulting in 73 peer-reviewed publications by four to eight NIH-funded major users. In 2006 Leica stopped manufacturing this model, and some parts are no longer available. There is not enough capacity on the existing confocal microscopes on the Storrs campus to accommodate the needs of the current users of the SP2 system in the event that a critical part cannot be replaced. Even if the existing instrument were to remain functional, many of the users critically need a 405 nm laser line to image the nuclear dye DAPI, along with the other fluorophores, but a 405 nm laser cannot be added to our existing SP2 unit. The other existing microscope on this campus with this capability is housed in a separate building and is too heavily used to accommodate our users' needs. The user group has grown from four NIH-funded investigators at the time of the original application in 2000 to eight major users and two minor users, and we have two new faculty members who will join our department this fall, whose research heavily depends on confocal microscopy. Confocal microscopy has now become an indispensable tool for the research program of the users in our department and a standard tool in cellular, molecular, and developmental neuroscience. Thus, there is a pressing need to acquire a new confocal system to ensure that the current users of the existing SP2 system have uninterrupted access to a functional confocal microscope and avoid delays in data collection and publication. The new confocal microscope will be housed in the center of the first floor of the Pharmacy Biology Building where the department is housed. It will be maintained by user fees and additional support from the Department, the Dean of the College of Liberal Arts and Sciences, and the Office of Vice President for Research.